In recent years, new light sources, such as LEDs and organic EL devices, are in growing demand as display devices, lightings, etc. with advantages such as low power consumption and low environmental burden. Particularly, LEDs are used for various electrical and electronic device products that are, for example, mobile communication equipment such as mobile phones, displays of personal computers, liquid crystal TVs or the like, console panels of automobiles and automobile interior lightings, traffic lights, and other household appliances.
Usually, an LED is composed of a semiconductor element (LED) that emits light, a lead wire, a reflector serving also as a housing, and a transparent sealing material for sealing the semiconductor element. Among these, the reflector is formed using various materials such as ceramic and heat-resistant plastic. However, the use of ceramic for the reflector causes problems of low productivity and low initial reflectivity. On the other hand, the use of heat-resistant plastic causes a heat resistance problem in the process of thermally curing a conductive adhesive and a sealing agent at 100 to 200° C. for as long as several hours, and a problem of light reflectance decrease caused by discoloration under the environment in which the reflector is used.
In recent years, the market for white LEDs is growing rapidly in applications such as lightings and liquid crystal display panels. In the reflectors used for such white LEDs, the brightness increases as the reflectance for light at an average wavelength of about 460 nm, which corresponds to the wavelength of a blue LED, increases, and thus the reflectors are required to have a high reflectance for light at an average wavelength of about 460 nm.
So far, it has been disclosed that as a polyamide resin composition that can be molded into, for example, a reflecting mirror such as a lamp reflector, a polyamide composition obtained by adding an inorganic filler having a specific average particle diameter to polyamide composed of dicarboxylic acid units containing 60 to 100 mol % of terephthalic acid units and diamine units containing 60 to 100 mol % of aliphatic alkylene diamine units having 6 to 18 carbon atoms has excellent heat resistance during moisture absorption, and excellent dimensional stability and surface smoothness, and moreover provides molded products having a beautiful surface appearance (see Patent Literature 1).
Also, as a material for a reflector for a light emitting device such as an LED, there has been proposed a resin composition for a reflector obtained by adding a specific amount of potassium titanate fiber and/or a specific amount of wollastonite to a specific semi aromatic polyamide (see Patent Literature 2). Without spoiling useful properties of the semi aromatic polyamide, this resin composition for a reflector has high level properties in terms of light reflectance, degree of whiteness, molding processability, mechanical strength, dimensional stability, heat resistance and moisture absorbency, and particularly has an excellent light shielding property, thereby capable of keeping the degree of whiteness without causing discoloration even when being exposed to a high temperature (see Patent Literature 2).
In addition, it has been proposed that by using a polyamide resin composition obtained by adding at least one reinforcement material selected from the group consisting of titanium oxide, magnesium hydroxide, a fibrous filler and an acicular filler to semi aromatic polyamide composed of dicarboxylic acid units containing terephthalic acid units and diamine units containing 1,9-nonanediamine units and/or 2-methyl-1,8-octanediamine units, it is possible to produce a reflector for an LED that is free from discoloration, keeps high degree of whiteness and has an excellent reflectance property in a visible light range even when being subject to a high temperature heat treatment simulating the manufacturing process of the LED (see Patent Literature 3).